It’s easy to become obsessed with the unsolved mysteries of this Earth. Most people like to think that anything can be figured out or solved… but that’s just not true.

Take these 7 mysteries, for example. They have been mysteries for decades (if not longer). No matter how many experts have examined the cases, they are still shrouded in mystery.

1.) The Aluminum Wedge of Aiud

In 1974, this is a wedge-shaped object found 1.2 miles east of Aiud, Romania. It was discovered on the banks of the Mures River. It was reportedly unearthed 35 feet under sand and alongside two mastodon bones. It looks like the head of a hammer and is made of an alloy of aluminum encased in a thin layer of oxide. It’s strange because aluminum was not discovered until 1808 and not produced in quantity until 1885. Since it was found in the same layer as mastodon bones, it would indicate that this wedge was at least 11,000 years old.

Many people believe that this wedge is evidence that aliens visited earth, since there is no way that humans created such an alloy so many thousands of years ago.

2.) The Babushka Lady

While people were pouring over the footage of the assassination of John F. Kennedy in 1963, a mysterious woman was spotted in the film. She was wearing a brown overcoat and a scarf on her head (a “babushka”). She appeared to be holding something in front of her face, like a camera.

She appeared many times in the footage and even stayed on the scene after most people left. Shortly after she is seen moving away to the East up Elm Street. The FBI publicly requested that the woman come forward and give them the footage she shot but she never did.

Even though frauds have come forward, today no one knows who the Babushka Woman is. We also don’t know why she was present at the shooting or why she refused to give up all of the evidence she was recording.

3.) Cicada3301

For the past three years, each January there is a bizarre, online puzzle game that is hosted by someone who calls themselves “3301.” Their symbol is a cicada. The complex puzzles draw on elements of cryptography, mathematics, literature, hidden messages, data security, and philosophy. Physical clues appear in places as diverse as Poland, Hawaii, Spain, Australia, and Korea. 3301 claims that its puzzles attempt to find “intelligent individuals.” They don’t say why.

Many believe these nearly impossible puzzles are a recruitment vehicle for organizations like the CIA or MI6.

4.) The Dighton Rock

The Dighton Rock is a 40-ton boulder located on the shores of the Taunton River in Massachusetts and it is covered in puzzling petroglyphs. For nearly 300 years, people have speculated about its origin and meaning. Investigators have attempted to decode the odd glyphs since an English colonist first described the boulder in 1680, but they have had little success.

In 1963, state officials removed the boulder and kept it for preservation. Most scholars think the stone carvings are of Native American origins. Some of the wilder theories have proposed that it was the work of the Portuguese, Chinese, or even the ancient Phoenicians.

5.) The Green Children

The Green Children of Woolpit were two children who appeared in the village of Woolpit in Suffolk, UK, in the 12th century. The brother and sister had green colored skin, even though they appeared normal in all other ways. They spoke an unrecognized language and refused to eat anything other than pitch from bean pods.

Eventually, their skin lost its green color. After they learned English, they explained that they were from the “Land of St Martin,” which was a dark place because the sun never rose far above the horizon. They claimed that they were tending their father’s herd and followed a river of light when they heard the sounds of bells. Then they arrived in Woolpit.

Some of the more unusual theories proposed for the origin of the children are that they were Hollow Earth children, parallel dimension children, or Extraterrestrial children.

6.) The Pollock Twins

In 1957, 11 year-old Joanna and 6 year-old Jacqueline Pollock were tragically killed in a car accident in Northumberland, England. They were sisters. A year later, their mother gave birth to twins Jennifer and Gillian.

The younger twin, Jennifer, had birth marks on her body in exactly the same place as Jacqueline had them. The twins then started requesting toys belonging to the deceased girls which they had no prior knowledge of. The twins even asked to go to a park they have never been to before (but their deceased sisters have).

A well-respected psychologist at the time, one Dr. Ian Stevenson, studied the case in-depth and concluded it was likely the twins were reincarnations of their departed sisters.

7.) The Zodiac Killings

“I like killing people because it is so much fun.”

That is how one of the many encrypted letters sent to San Francisco newspapers began, sent by the man who called himself the Zodiac. For most of 1969, a serial killer terrorized Bay Area residents, killing five and possibly more. It started when a couple was shot to death while sitting in a car on a lover’s lane on Dec. 20, 1968.

Over the next 10 months, the killer would strike again, shooting a couple in a public park, trussing up and stabbing yet another man and woman near a peaceful lake, and shooting a cabdriver in the head.

The Zodiac killer toyed with police and reporters the whole time. He called in several of the murders and began to send coded letters to newspapers, using a cross within a circle as his symbol. At one point, he mailed in a piece of bloodied shirt to prove he was who he claimed to be. Another time, he threatened to shoot up a school bus full of children. The investigation went on for years.